Effects of optical sensing based variable rate nitrogen management on yields, nitrogen use and profitability for cotton

Abstract

This research evaluated the profitability and nitrogen (N) efficiency of real time on-the-go optical sensing measurements (OPM) for variable-rate (VRT) N management for cotton. Two forms of OPM-based VRT N management and the existing farmer practice (FP) were used to determine N rates applied to cotton on 21 farm fields in the lower Mississippi River Basin states of Louisiana, Mississippi, Missouri and Tennessee, USA. A modified version of the Schabenberger and Pierce on-farm experimentation model was used to evaluate VRT N management and landscape, soil and weather factors on lint yields, N rates, N efficiency (lint yield divided by N rate) and net returns. Field level mean lint yields were not different between VRT and FP. VRT decreased N rates applied on four fields and increased N rates applied on four other fields. However, landscape, soil and weather attributes specific to fields influenced VRT N rates. VRT N rates were similar to FP N rates on the other fields in the study. N efficiency was not improved with VRT N management. N rates were not low enough to increase N efficiency. Changes in lint yields and N rates due to VRT coupled with USDA NRCS Environmental Quality Incentive Program cost-share payments were not sufficient to produce higher net returns relative to FP N management at the field level. In this multi-site, multi-year study, yields and net returns from VRT were not different from FPs which did not utilize variable rate N management.